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Influence Of Transition Metal Doping On Cathode Material Structure And Electrochemical Performance For Li/MnO2Battery

Posted on:2015-11-22Degree:MasterType:Thesis
Country:ChinaCandidate:Q L LiuFull Text:PDF
GTID:2181330431470474Subject:Chemistry
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Electrolytic manganese dioxide (EMD), as a kind of cathode material which is widely used in Li/MnO2battery in the industrial production, the influences of heat treatment temperature on its structure and electrochemical properties have been studied clearly for passed years. Another important factor which affect its structure is the time, this is detailed studied in the chapter two in this paper. In the second chapter, the EMD samples are heat treated at325℃,350℃and375℃for10h,20h respectively, and heat treated at400℃for1h,2h,10h respectively. Then the physical and electrochemical performances are tested to study the effects of temperature and the time on the structure and electrochemical performance of EMD. The conclusions are:(1) The structure and the crystal form of EMD not only greatly influenced by the temperature, but also influenced by the heating rate and the heating time.(2) The samples heat treated under350℃for10h and under400℃for1h have better electrochemical performance than others, suggesting that samples heat treated at low temperature for a long time and at high temperature for a short time both have better electrochemical performance;(3) the research results can be used in industry to reduce production cost and upgrade production efficiency.In chapter three, Fe2O3doped MnO2(Fe-HEMD) with various mole percents had been synthesized via a simple solid-state synthesis using electrolytic manganese dioxide (EMD). The influence of Fe2O3doping on the structure and electrochemical properties are studied. The conclusions are:(1) the prepared Fe-HEMD samples are mixed crystal phase of y-MnO2and β-MnO2, and the doped Fe2O3has not changed the crystal forms of MnO2. The changes of lattice parameters occurred in Fe-HEMD, indicating that some Fe2O3are doped into MnO2structure.(2) The doping of Fe can not enhance the discharge capacity of MnO2material at low discharge rate (0.1mA cm-2). While it can effectively improve the Li-storage in MnO2at a high discharge rate (2mA cm-2), in which Fe-HEMD-6electrodes exhibit the best capacity of164.6mAh g-1. This can be attributed to the larger Li+diffusion cross section, shorter Li+migration path and more space to accommodate Li+for Fe-HEMD-6.In order to overcome the shortage of the electrochemical properties of Fe-HEMD, in chapter four, we choose Sc and Ti as doping element which are in the same period with V other than V. In order to overcome the nonuniform and agglomerated of the product prepared by solid-state synthesis, an ambient temperature redox synthesis method followed by ultrasonic is used to obtain pure and Sc2O3, TiO2, V2O5single doped MnO2. The conclusions are:(1) The pure and doped MnO2samples all crystallize in y+P-MnO2structure. The morphology and specific surface area was improved obviously,, and the TiO2doped one has the highest surface area of106.60m2g-1(2) All the doping samples are effective in improving specific discharge capacities and voltage platforms.(3) The outstanding electrochemical properties can be attributed to the combined action of higher surface area, higher ko, higher DLi and smaller Rct. we conclude that the electrochemical reaction process is propably a mixed-controlled reaction.(4) The doping samples have better structural stability due to their stronger bond energy of Mn-O and smaller cell volume expansion during discharge.(5) A model is proposed to describe the structural change in different depths of discharge.To sum up, this paper mainly includes three parts.(1) The influence of heat treatment temperature and time on EMD structure and electrochemical properties have been studied, we find the time is an important factor. It suggests that samples heat treated at low temperature for a long time and at high temperature for a short time both have better electrochemical performance.(2) Fe2O3doped MnO2(Fe-HEMD) with various mole percents had been synthesized via a simple solid-state synthesis using electrolytic manganese dioxide (EMD). The influence of Fe2O3doping on the structure and electrochemical properties are studied. The increase of the discharge capacity of Fe-HEMD is limit, but it has close relationship to the Li+diffusion cross section, Li+migration path and space to accommodate Li+.(3) An ambient temperature redox synthesis method followed by ultrasonic is used to obtain pure and Sc2O3, TiO2, V2O5single doped MnO2. The morphology and structure and electrochemical properties are improved obviously. Especially for the TiO2doped one; and a model is proposed to describe the structural change in different depths of discharge.
Keywords/Search Tags:Electrolytic manganese dioxide, Doping, Li/MnO2battery, Electrochemicalperformance
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